Laser acceleration of absorbing particles

Tirtha Mitra, Andrew K. Brown, David M. Bernot, Sage Defrances, and Joseph J. Talghader

A Yb-doped fiber laser is used to accelerate and evaporate absorbing particles in air. Optical intensities of 1MW/cm2 and 2MW/cm2 illuminate stainless steel particles. These particles are accelerated to velocities of tens of meters per second before evaporating within a few tenths of a millisecond. Position measurements are made using direct imaging with a high-speed camera. A fundamental system of coupled differential equations to track particle momentum, velocity, mass, radius, temperature, vapor opacity, and temperature distribution is developed and shown to accurately model the trajectories and lifetimes of laser heated particles. Atoms evaporating from the particle impart momentum to the larger particle, which accelerates until it is slowed by drag forces. Heat transfer within the evaporating particles is dominated by radiation diffusion, a process that usually only dominates in astrophysical objects, for example in the photospheres of stars.

DOI